1. Field of the Invention
The present invention relates to a desulfurizing method for removing a sulfur component from a molten iron alloy.
2. Description of the Related Art
The need for high quality steel has generated a demand for low-sulfur steel. There are two types of processes for removing sulfur (hereinafter referred to as desulfurization); one carried out during the molten (pig) iron stage in a torpedo car or a molten-iron pan, and the other carried out in the molten-steel stage on dioxidized molten steel downstream of a converter. The former is the most prevalent desulfurization process today due to improved molten-iron pretreatment techniques.
Desulfurization in the molten-iron stage employs a CaO-based desulfurizing agent, an Na.sub.2 O-based desulfurizing agent, an Mg-based desulfurizing agent, or similar suitable agent. The CaO-based desulfurizing agent is preferred the cost and ease of slag treatment after desulfurization. To this end, an improved process for desulfurizing molten iron with a CaO-based desulfurizing agent is desired.
A known process for desulfurizing molten iron with a CaO-based desulfurizing agent uses a rotating agitator to draw the desulfurizing agent into the molten iron.
Japanese Unexamined Patent Application Publication No. 55-76005 discloses a method of accelerating the desulfurizing reaction in which a hydrocarbon gas is blown into the molten iron through the agitator. However, as a result of studying the disclosed method in detail the inventors found that the hydrocarbon gas blown into the molten iron through the agitator is concentrated at the center of rotation due to a density difference between the molten iron and the gas.
This technique also increased the cost of the process because a passage for the hydrocarbon gas must be provided in the agitator and special piping and joints are required to supply the gas to the agitator, which is a rotating body.
Japanese Unexamined Patent Application Publication No. 8-337807 discloses a method of accelerating the desulfurizing reaction by simultaneously blowing a powdery desulfurizing agent into molten iron and blowing a reducing gas onto the bath surface of the molten iron. However, the surface area in which the desulfurizing agent floats is variable depending on ablation of a lance used for blowing the desulfurizing agent or deposition of the metal or slag. This presents the problem of precisely blowing the reducing gas to the area in which the desulfurizing agent floats.